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The Science of Fear

Updated Monday, 10 October 2022

Recoil at the number 13? Scream at spiders? At some point, we all get scared. But why, and how? This article explores the science behind fear.

Little miss muffet screaming at a spider A fear of spiders is one of the common phobias Does the feeling of fear reside in the body or the brain? That is, do we first react to something with our bodies, notice our reaction and accordingly feel fear, or do we consciously acknowledge that something is threatening and then react accordingly with our bodies?

Logically, fear is registered by the brain before the body reacts - how else can the body process the information to decide that a fearful event is happening? The question, then, is: 'What gives rise to the feeling of fear - does the initial, essentially pre-conscious, perception cause a conscious feeling (brain then body), or does the body react first and then the perception of that response give us the feeling (body then brain)?'

...scary stuff!

I've seen a man try to overcome his phobia of snakes. Surely his fear is due to his brain recognising the visual image of a snake and then 'telling him' to become scared - with all the physical manifestations that take place when you become fearful? But why can't he just tell himself that the snake isn't dangerous? He finds it almost impossible to 'turn off' his fear, even when it is irrational. It seems that some 'emotional centre' in his brain doesn't readily listen to his 'reasoning' brain.

In a previous the programme on fear with the BBC, I looked at my fear of heights, where my body's reaction to the experience leads to feelings of fearfulness and panic. Is it my gut feeling, and the sense of hair standing on end at the back of my neck that makes me feel afraid? I'm not sure that we will work this out, but by having a go, we may begin to understand more about our own fears and phobias.

Darwin and Fear

In his wonderful book 'The Expression of the Emotions in Man and Animals', Charles Darwin tries to explain the evolutionary advantage of the reactions we have to various situations, like those of grief, anxiety, helplessness, surprise and fear. He compares our behaviour with similar responses in animals, concluding that many emotional reactions are shared with other species and have useful functions, such as helping us to react quickly in a fearful situation.

Friday 13th on a calendar The fear of Friday the 13th is called paraskevidekatriaphobia He makes a useful distinction between 'fear' and 'terror'. He suggests that the word 'fear' is appropriate for our reaction to something sudden and dangerous. He uses the word 'terror' for extreme fear, in which there is trembling of the vocal organs and shaking of the body, like Zeron experienced. Nevertheless, whether it's 'terror' or 'fear' it's still an unpleasant emotion.

Darwin observed that when we suddenly become scared, our mouth often opens. He argued that an open mouth may have the advantage of allowing us to breathe more freely in preparation for 'fight or flight'. He had realised that many of the expressions we use, and the reactions we have to fear, have been conserved through the generations since prehistoric times - in fact, probably since before we were human.

Together with cold sweats, the ceasing of anal sphincter control (yes, people do shit themselves with fear), and the erection of bodily hair by 'the muscles of fright' (minute, involuntary muscles, which run to each separate hair follicle) - we have lots of vestigial, or "leftover", fear responses from our prehistoric ancestors. The best example is that bristling hair. It is still believed that our hair standing on end is a throwback to when our ancestors had fur. Darwin explains it as follows:

"With respect to the involuntary bristling of hair, we have good reason to believe that in the case of animals this action, however it may be originated, serves, together with certain voluntary movements to make them appear terrible to their enemies, and as the same involuntary and voluntary actions are performed by animals nearly related to man, we are led to believe that man has retained through inheritance a relic of them, now become useless."

One point Darwin missed is that hair standing-up on end is not totally useless; they will be more sensitive to air currents and pick up movements of a predator - or enemy - through the detection of a slight breeze or draught.

Of course there are some things that Darwin couldn't quite explain - for example, why people cover their mouths or the top of their heads when startled, although he did note that "the hand being placed over the mouth or on some part of the head has been observed in so many races of man that it must have some natural origin".

It's possible that placing the hand over the mouth may be to reduce the sound our breathing makes - reducing noise that can be detected by an enemy/predator. Having the hands above the shoulder near the head, might also help to protect this vital organ, or if we are attacked, they might be useful in this position to provide force and accuracy when moved downwards to hit a predator or enemy. They also provide balance in case sudden movement is required.

So what's the point of all this about the origin of fear? Well, there's so much evidence suggesting that our reactions to fear are comparable to that of distant ancestors and primitive animals, that it can help us pinpoint where the feeling comes from. It must be the primitive part of our brain - the 'lower brain' - which is responsible for our rapid response to fear, as the 'higher brain' only appeared comparatively recently in our evolution.

The Brain

The human brain is very highly developed. Many people would argue that its size and complexity are the vital features that make us human. It is also quite complex, so a diagram is shown below:

A diagram of the human brain The human brain

In the image above:
A) View of the middle surface of right side of the 'higher' brain showing several major structures.
B) Enlarged view of the brain structures that form the 'limbic system' - note the prominent size and position of the amygdala.

The brain stem (which lies below the brain regions shown in Figure A) is the oldest part of the brain, and messages pass to and from it without the need for conscious thought. This area is lower in the head and is also called the 'lower brain', because it consists of parts similar to those found in some very primitive creatures.

The cortex makes up part of the 'higher brain'. It is a highly folded sheet of nerve cells about 3mm thick covering the outer part of the brain, and is the region of the brain that is most noticeably expanded in humans. The limbic system, which includes the amygdala, lies between the cortex and the brain stem - the major parts of the limbic system are shown in Figure B.

The Amygdala

The amygdala is an almond-shaped structure contained within the limbic structures of the brain, and is located at the base of the temporal lobe (see B in the image above). To the non-expert, this means that it is about level with the top of the ears and about half way towards the centre of the head. Recent research, using sophisticated equipment which maps the parts of the human brain that are active during particular tasks, has revealed that the amygdala is a very important neural centre involved with the expression of emotions - particularly fear. Unfortunately, some individuals who have a damaged amygdala have trouble feeling fear - they also lack the ability to recognise fear from the facial expressions of other people.

It turns out that the amygdala plays a critical role in the chain of events where a person (or animal) is able to recognise a threat from stored information of previous experiences - that is, from memory. The retrieval of this emotional information allows people to act quickly - without necessarily thinking. It also turns out that conscious thought can influence emotions - for example, the straight face of a poker player with a lousy hand!

'To fight or not to fight'

Here are some interesting facts:

• Our body releases its own natural painkillers, called endorphins, to cope with injuries sustained during fight or flight.

• Our blood vessels near the skin become constricted, reducing blood loss should you be injured.

• Our sweat glands open, even when you are cold, ready to cool you should you need to run or fight.

• Our pupils dilate, to help us detect movement.

• Our hairs stand on end - so we become more sensitive to our environment.

• Our heart rate increases, our arteries constrict to allow maximum pressure of blood to the body, and our veins dilate to allow blood to return as quickly as possible to the heart. The result is that we go from pumping one gallon of blood, through our hearts, per minute to five gallons per minute. This is to make sure that our muscles will get as much oxygen as possible, should they need it.

• The respiratory system gears up for 'heavy breathing' should you need to run or fight.

• Glucose is released from the liver to create instant fuel.

• Blood vessels to the digestive and reproductive systems, and kidneys become constricted, thus shutting down unnecessary systems. Also, our mouths dry up. When fighting or running for your life, eating and sex will be the last thing on your mind.

• The vital blood supplies are diverted towards the main muscles of the legs and arms etc, as well as the brain. You need plenty of blood for the 'fast thinking' you might need to do - not much point in having energy in your muscles if you run in the wrong direction!

• Contents of the stomach/bowel/bladder may be jettisoned. This could distract the attacker and 'lightens the load' the body has to carry in escape.

The 'fight or flight' mechanisms listed above were invaluable in primitive times, when hunting prey or escaping from predators, and were essential daily activities; however, in a modern society they can cause problems; it's sometimes useful to have a fast thinking brain, but running over the horizon to escape a sabre-toothed tiger is less often required.

If you become stressed when working in an office, the 'fight or flight' response can take a toll on your heart and your general health because they are acting inappropriately for the conditions in which you find yourself. Because of this, over the long-term, stress can cause severe heart problems and other life threatening conditions. Since the stress response gets you ready for strenuous physical exercise, the best way to counteract it is to actually take some exercise. Exercise helps the body relax and uses up those dangerous chemicals that will otherwise carry on circulating in your blood. Strangely, a side benefit to fighting stress with exercise is you'll improve your fitness - an ideal antidote to modern living. So my advice is, if you have a stressful life - take more exercise with it!

Zeron overcomes his fear of snakes

So what is fear and why do we react that way?

I hope you've now got a better idea how your body and brain both perceive, and react to, fear. If you are interested in finding out more, why not see what courses The Open University offers. Even if you've done no biology before, a foundation course will really open your eyes to what is going on around you in the natural world, and how our bodies work.

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